Dam Break Studies for Gandhi Sagar and Rana Pratap Sagar Dams

B P Roy, Member J N Nanda, Non-member Cusat Digital Library Service http://dspace.cusat.ac.in/

Protecting the public from the consequence of dam failures has taken on increasing importance as population has concentrated in areas vulnerable to dam break disasters. This has created general interest in the dam safety analysis in recent years. There is codal provision (IS code 11223-1985) for insisting on dam break studies. The preventive measures in avoiding dam disaster are either issuing flood warning to the public downstream, or regulating reservoir in such a fashion so that there may not be hydrologic dam failure. These are difficult during the time of occurrence, and hence hypothetical situation is a necessary exercise. The United States National Weather Services DAMBRK' program attempts to represent the current state-of-the- art in understanding dam failures and utilising hydrodynamic theory to predict the dam break wave formation and downstream progression. This paper presents the use of DAMBRK' program in finding the inflow hydrograph at dam site improbable maximun flood condition, using the distributed model. The same program has been used to find the safe impingement level in probable maximum flood condition for Gandhi Sagar Dam and to visualise the downstream situation under different dam failure conditions.

Keywords : Distributed model; Dynamic routing; Safe impingement level; Inflow hydrograph; Outflow rating INTRODUCTION In the first stage, Gandhi Sagar Dam, a 63.7-m high masonry More and more dams have come up, or are being constructed, dam for a gross storage of 7746 Mm 3 of water and hydro- with the aim of using the available water resources optimally power station with an installed capacity for generating 119 for developmental purposes, or for protecting lives and MW of power, along with were completed in properties from the fury of floods. With the assured water November, 1960. In the second stage the 44.8-m high Rana resources facility and flood protection provided by the dam, Pratap Sagar Dam, at in , about 48 km the increase in population and the encouragement for im- downstream of Gandhi Sagar Dam and 48 km upstream of proving the overall economy of the country have led to Kota Barrage, with a gross storage of 2899 Mm 3 water and various developmental activities downstream of the dam. a powerhouse with an installed capacity of 172 MW were This has resulted in the settlement of large population and completed in 1970. In the third stage, the 44.8-m high properties on the flood plain and adjoining areas. However, to create a head of 36.5 m for power. in the eventuality of a dam failure, the disaster would be generation only, with an installed capacity of 99 MW was catastropic with the flood flow not only occupying the completed in 1972 about 26 km upstream of Kota Barrage. erstwhile flood plain area, but the area adjoining it. Fig 1 shows the location of the various projects. The dam break analysis involves the following component For Gandhi Sagar Dam, it was informed that design flood steps : has exceeded ten times since date of completion. Rana Pratap development of identification of the inflow Sagar Dam is hydrologically related with Gandhi Sagar hydrograph to the reservoir at the time of failure, Dam, hence, hydrological safety of both the dams were con- ducted. This paper presents the general principles behind the routing the inflow hydrograph through the reservoir, mathematical models used for dam break analysis, discusses development of the failure condition of the dam, the various available models for darn break analysis and their calculating the outflow hydrograph from the failed special features. Also a brief description of a case study of dam, and dam failure using US National Weather Services DAMBRK model is presented. (v) modelling the movement of the flood wave downstream to determine the magnitude of maxi- RATIONALE FOR THE STUDIES mum discharge and maximum water level, and their The Gandhi Sagar Dam has been designed to accommodate arrival time, inundated area, etc. a design peak flood inflow of 212 000 cumecs. This design This study has been carried for Gandhi Sagar and Rana flood has been exceeded on at least 10 occasions since 1960 Pratap Sagar Dams of Chambal Basin. The Chambal Valley (Table 1). Development Project was conceived and executed in three In respect of , the design flood of stages as a joint venture of the Governments of Rajasthan 184 000 cumecs was derived on the basis of the maximum and . The various projects under this release of 136 000 cumecs from Gandhi Sagar Dam and a development programme in different stages are as given maximum discharge of 5900 cumecs from the intermediate here. catchment as worked out from Inglis formula. As Gandhi B P Royis with National Institute of Hydrology, Roorkee 247 667 and Sagar and Rana Pratap Sagar dams are in a sequence, any J N Nanda is with Planning Commission, New Delhi. change in Gandhi Sagar will affect Rana Pratap Sagas. This This paper (revised) was received on July 7, 1995. Written discussion on the necessitated a review of design flood. Over and above, it was paper will be entertained till June 30, 1997. felt that dam break studies of Gandhi Sagar and Rana Pratap Vol 78, May 1997 7